U.S. patent number 5,629,494 [Application Number 08/609,270] was granted by the patent office on 1997-05-13 for hydrogen-less, non-azide gas generants.
This patent grant is currently assigned to Morton International, Inc.. Invention is credited to Michael W. Barnes, Robert D. Taylor.
United States Patent |
5,629,494 |
Barnes , et al. |
May 13, 1997 |
Hydrogen-less, non-azide gas generants
Abstract
A gas generant composition contains no hydrogen, using as the
major fuel component cupric and/or zinc bitetrazole and as a major
oxidizer component CuO and/or Fe.sub.2 O.sub.3. A minor fuel
component may be a salt of dicyanamide which reduces processing
sensitivity of the composition. A minor oxidizer component may be a
nitrate, chlorate, or perchlorate salt.
Inventors: |
Barnes; Michael W. (Brigham
City, UT), Taylor; Robert D. (Hyrum, UT) |
Assignee: |
Morton International, Inc.
(Chicago, IL)
|
Family
ID: |
24440066 |
Appl.
No.: |
08/609,270 |
Filed: |
February 29, 1996 |
Current U.S.
Class: |
149/36;
149/109.2 |
Current CPC
Class: |
C06D
5/06 (20130101) |
Current International
Class: |
C06D
5/00 (20060101); C06D 5/06 (20060101); C06B
047/08 () |
Field of
Search: |
;149/109.2,119,36 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Jordan; Charles T.
Assistant Examiner: Hardee; John R.
Attorney, Agent or Firm: Nacker; Wayne E. White; Gerald
K.
Claims
What is claimed is:
1. A hydrogen-less gas generant composition consisting essentially
of
A) between about 20 and about 40 wt % of a fuel and B) between
about 60 and about 80 wt % of B) an oxidizer, said weight
percentages of A) and B) being calculated on the total weight of A)
plus B),
between about 60 and 95 wt % of said fuel A) comprising a fuel
component i) selected from the group consisting of cupric
bitetrazole, zinc bitetrazole and mixtures thereof, and
between about 5 wt % and about 40 wt % of said fuel A) comprising a
fuel component ii) selected from the group consisting of cupric
dicyanamide, zinc dicyanamide and mixtures thereof,
between about 70 and 100 wt % of said oxidizer B) comprising an
oxidizer component iii) selected from the group consisting of CuO,
Fe.sub.2 O.sub.3, and mixtures thereof, and
up to about 30 wt % of said oxidizer B) comprising an oxidizer
component iv) selected from the group consisting of alkali and
alkaline metal salts of nitrate, chlorate, perchlorate, and
mixtures thereof.
2. A gas generant composition in accordance with claim 1 wherein
said fuel component i) is cupric bitetrazole.
3. A gas generant composition in accordance with claim 1 wherein
said fuel component ii) is zinc bitetrazole.
4. A gas generant composition in accordance with claim 1 wherein
said oxidizer component iii) is cupric oxide.
5. A gas generant composition in accordance with claim 1 wherein
fuel component ii) is cupric dicyanamide.
6. A gas generant composition in accordance with claim 1 wherein
fuel component ii) is zinc dicyanamide.
Description
While the major portion of gas generants in use today for inflating
automotive airbags are based on azides, particularly sodium azide,
there has been a movement away from azide-based compositions due
toxicity problems of sodium azide which poses a problem for
eventual disposal of un-deployed units. Non-azide formulations are
described, for example, in U.S. Pat. Nos. 5,197,758; 3,468,730;
4,909,549; 5,035,757, 3,912,561; 4,369,079 and the teachings of
each of which are incorporated herein by reference.
However, non-azide formulations often have their own problems,
tending to produce undesirable gases (as opposed to azide which
produces only nitrogen upon combustion) and/or high levels of
particulates and/or extremely high combustion temperatures (the
latter particularly problematic when utilizing aluminum inflator
housing or other aluminum parts). While numerous non-azide
pyrotechnic compositions have been suggested for inflating passive
automotive restraint systems, the majority of these compositions
contain hydrogen. One undesirable combustion gas is ammonia, which
tends to be produced by hydrogen-containing compositions formulated
to burn at moderate temperatures. To reduce the level of ammonia
produced, it is known to increase the oxidizer-to-fuel ratio; but
this tends to raise the level of nitrogen monooxide and/or nitrogen
dioxide to unacceptably high levels, necessitating a balancing act
which cannot easily be performed with consistency.
One way to avoid the ammonia/NO.sub.x balancing act is to formulate
without hydrogen and to burn at moderate temperatures.
Above-referenced U.S. Pat. Nos. 4,369,079 and 4,370,181 are based
upon the use of alkali or alkaline earth metal salts of
bitetrazoles as fuels. Unfortunately, the compositions of these
patents tend to produce solid particulates which are difficult to
filter. Particulates may be harmful to vehicle occupants,
particularly asthmatics. Also, particulates released to the vehicle
interior during airbag deployment give the appearance of smoke and
the specter of fire.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a
non-azide gas generant in which neither the fuel nor oxygen
contains hydrogen, which burns at relatively moderate temperatures,
and which produces an easily filterable slag. The gas generant
composition comprises between about 20 and about 40 wt % of A), a
fuel and between about 60 and about 80 wt % of B) an oxidizer, said
weight percentages of A) and B) being based on the total weight of
A) plus B). Between about 60 and 100 wt % of the fuel A) comprises
a fuel i) selected from the group consisting of cupric bitetrazole,
zinc bitetrazole and mixtures thereof; and up to about 40 wt % of
the fuel A), preferably at least about 15 wt % of the fuel A)
comprises a fuel ii) selected from the group consisting of an
alkali metal salts of dicyanamide, an alkaline earth metal salt of
dicyanamide, a transition metal salt of dicyanamide and mixtures
thereof. Between about 70 and 100 wt % of the oxidizer B) comprises
an oxidizer iii) selected from the group consisting of CuO,
Fe.sub.2 O.sub.3, and mixtures thereof, and up to about 30 wt % of
the oxidizer, preferably at least 10 wt % of the oxidizer, selected
from the group iv) consisting of alkali and alkaline metal salts of
nitrate, chlorate, perchlorate and mixtures thereof.
Detailed Description of Certain Preferred Embodiments
The primary fuel component i) is cupric bitetrazole, zinc
bitetrazole or a mixture thereof. These fuels provide a high burn
rate and, upon combustion, produce easily filterable copper metal
and/or ZnO, respectively. Thus, these transition metal salts of
bitetrazole are advantageous over alkali and alkaline earth metal
salts of bitetrazole which produce particulates that are not easily
filtered, and which, upon combustion and inflation of an airbag,
fill a passenger compartment with particulates. Cupric bitetrazole
is the preferred fuel component i). Neither cupric nor zinc
bitetrazole contain hydrogen which can result in the formation of
ammonia. Consequently, the compositions of the present invention
can be formulated with an appropriate fuel-to-oxidizer ratio so as
to minimize the production of NO.sub.x, particularly NO and
NO.sub.2, so as to provide an acceptably low level of these gases
in the combustion gases.
While fuel component i) may be used alone, i.e., used at 100% of
the fuel A); cupric and zinc, particularly cupric, bitetrazole are
very friction-sensitive. Accordingly, it is preferred to utilize a
second fuel component ii), which like component i) does not contain
hydrogen, and to this end, the dicyanamide salt is utilized.
Preferred cations for the dicyanamide salt are cupric, zinc, and
sodium, cupric and zinc being preferred over sodium, and cupric
being the most preferred. At levels as low as 5 wt % of the fuel
A), fuel component ii) reduces the friction-sensitivity of
component i). Preferably, component ii) is used at at least about
15 wt % of the fuel A).
The major oxidizer component iii), like the fuel component(s) i)
and ii) is selected for producing an easily filterable slag. Cupric
oxide (CuO) is the preferred major oxidizer component iii),
producing easily filterable copper metal upon combustion.
While oxidizer component iii) may be used as the sole oxidizer,
i.e., at 100 wt % of the oxidizer B), the secondary oxidizer iv) is
used to improve low temperature ignition and increase gas output
level. If used, oxidizer component iv) is generally used at a level
of at least about 5 wt % of the oxidizer B), preferably at least
about 10 wt %. It is preferred that oxidizer component iv) not be
used at a high level so as to minimize its impact on filterability
of the combustion products. Preferred secondary oxidizers are
nitrates, particularly strontium, sodium and potassium.
To minimize production of NO.sub.x, the stoichiometric oxidizer to
fuel ratio is between about 1.0 and about 1.3, preferably between
about 1.05 and about 1.15. Herein, an oxidizer to fuel ratio of 1.0
is defined as being precisely enough oxidizer to oxidize the fuel
to carbon dioxide, nitrogen, water and the appropriate metal or
metal oxide. Thus in a formulation where the oxidizer to fuel ratio
is 1.05, there is a 5 molar percent excess of oxidizer, and so
forth.
While the compositions of the present invention have a number of
advantages, including low levels of toxic combustion gases,
relatively low burn temperatures which are consistent with use in
inflators having aluminum housings and/or other aluminum
components, and produce readily filterable slag; the compositions
do utilize sensitive fuel components. As noted above, the major
fuel component i) has high friction-sensitivity, and the dicynamide
salts, particularly cupric dicyanamide, tend to be very sensitive
to electrostatic initiation. The sensitivity problems, however, can
be adequately addressed by appropriate processing of the generant
compositions, particularly by aqueous processing. The generants are
preferably manufactured by wet mix/granulation or by mix/spray
drying followed by pressing, e.g., into cylindrical pellets. The
size and shape of prills or tablets is determined by the ballistic
response needed in an inflator design. A typical cylindrical pellet
is 0.25 in. diameter, 0.08 in. long.
Gas generant compositions in accordance with the invention may be
formulated with only the fuel A) and oxidizer B). However, in
addition to the fuel A) and oxidizer B), minor components, such as
coolants, pressing aids, , as are known in the art may also be
added, typically at levels no greater than about 5 wt % relative to
the total of fuel A) plus oxidizer B). Like the fuel A) components
i) and ii) and oxidizer B) components iii) and iv), any additional
minor components used should contain no hydrogen.
The invention will now be described in greater detail by way of
specific examples.
Examples 1-4
The following compositions were formulated in accordance with the
invention. Percentages are by weight of total composition,
percentages of fuel or oxidizer in parenthesis.
______________________________________ Component Example 1 Example
2 Example 3 Example 4 ______________________________________ Cupric
bite- 21.87 (68.6) 18.37 (63.6) 20.88 (66.4) 45.14 (100) trazole
Sodium di- 10.50 (36.4) 10.56 (33.6) -- cyanamide Cupric di- 10.0
(15.1) cyanamide Cupric oxide 56.13 (84.9) 60.63 (85.2) 58.00
(84.6) 44.86 (81.8) Strontium 10.00 (15.1) 10.50 (14.8) 10.56
(15.4) 10.00 (18.2) nitrate
______________________________________
Compositions 1 was prepared by preparing a slurry of cupric
bitetrazole in water by the reaction of cupric oxide with
bitetrazole dihydrate according to the equation:
and a slurry of cupric dicyanamide in water by the reaction of
cupric nitrate with sodium dicyanamide according to the
equation:
The 2 slurries were combined and additional material was added as
required for the formulation. Mixing was completed using a high
shear mixer. The mixture was dried until it could be pressed
through a 6 mesh screen and then drying was completed.
More specifically, bitetrazole dihydrate (4.32 gm) was dissolved in
8.3 ml. of water by heating to approximately 80.degree. C. Cupric
oxide (14.9 gm) was added, the mixture was hand-stirred, and then
the mixture was heated on a water bath at 80.degree. C. for
approximately one hour with occasional stirring by hand. Sodium
dicyanamide (2.5 gm.) was dissolved in 8.3 ml. of water. Cupric
nitrate (3.27 gm) was added slowly portion-wise with stirring to
produce a blue precipitate of cupric dicyanamide. It was heated on
the water bath at 80.degree. C. for approximately one hour. The two
slurries were combined and mixed on a Proline.RTM. model 400B
laboratory homogenizer for approximately 5 min. The slurry was
dried in a vacuum oven for approximately 3 hours at 85.degree. C.
and granulated by pressing through a 6 mesh screen and drying was
completed in the vacuum oven for an additional two hours.
The composition had a burn rate of 0.8 inches per second as
measured by burning a pressed slug of material in a closed bomb at
100 psi. The friction sensitivity of the formulation as measured on
BAM friction test apparatus was 120 newtons. Other safety tests
results were acceptable according to internally set standards.
The table below gives the measured/calculated results for
hydrogen-less gas generants in accordance with the invention.
Results show that it is preferred to utilize a dicynamide salt as a
co-fuel with the bitetrazole salt (Examples 2 and 3) to mitigate
friction sensitivity.
______________________________________ Composition Example 2
Example 3 Example 4 ______________________________________ Friction
sensitively 160 120 20 (Newtons) Burn rate (inches/sec. 0.8 0.83
(ips)) Theoretical gas yield 1.14 1.02 (moles 100 gm) Theoretical
combustion 1550 1517 temp. (.degree.Kelvin)
______________________________________
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